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Mon, 30 Dec 2024 10:59:58 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id Tud/Ly59cmeFbQAAD6G6ig (envelope-from ); Mon, 30 Dec 2024 10:59:58 +0000 Date: Mon, 30 Dec 2024 11:59:58 +0100 Message-ID: <87pll9wi4x.wl-tiwai@suse.de> From: Takashi Iwai To: Kun Hu Cc: Takashi Iwai , perex@perex.cz, tiwai@suse.com, linux-sound@vger.kernel.org, linux-kernel@vger.kernel.org, "jjtan24@m.fudan.edu.cn" Subject: Re: Bug: slab-out-of-bounds in snd_seq_oss_synth_sysex In-Reply-To: <3326E7C2-1E4F-4F57-AAB5-065C20854F31@m.fudan.edu.cn> References: <2B7E93E4-B13A-4AE4-8E87-306A8EE9BBB7@m.fudan.edu.cn> <87ed1qydgi.wl-tiwai@suse.de> <3326E7C2-1E4F-4F57-AAB5-065C20854F31@m.fudan.edu.cn> User-Agent: Wanderlust/2.15.9 (Almost Unreal) Emacs/27.2 Mule/6.0 Precedence: bulk X-Mailing-List: linux-sound@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-Spam-Score: -3.30 X-Spamd-Result: default: False [-3.30 / 50.00]; BAYES_HAM(-3.00)[100.00%]; MID_CONTAINS_FROM(1.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-0.999]; MIME_GOOD(-0.10)[text/plain]; RCPT_COUNT_SEVEN(0.00)[7]; RCVD_VIA_SMTP_AUTH(0.00)[]; TO_DN_EQ_ADDR_SOME(0.00)[]; MIME_TRACE(0.00)[0:+]; ARC_NA(0.00)[]; RCVD_TLS_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FUZZY_BLOCKED(0.00)[rspamd.com]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo] X-Spam-Flag: NO X-Spam-Level: On Mon, 30 Dec 2024 10:47:08 +0100, Kun Hu wrote: > > > The only place incrementing sysex->len is that loop and it has already > the bounce check which resets sysex->len to 0. That is, the likely > reason of the buffer overflow is rather the racy calls of this > function. > > If so, a potential fix would be rather to protect the concurrency, > e.g. a simplest form is something like below. > Could you check whether it addresses your problem? > > thanks, > > Takashi > > -- 8< -- > --- a/sound/core/seq/oss/seq_oss_synth.c > +++ b/sound/core/seq/oss/seq_oss_synth.c > @@ -66,6 +66,7 @@ static struct seq_oss_synth midi_synth_dev = { > }; > > static DEFINE_SPINLOCK(register_lock); > +static DEFINE_MUTEX(sysex_mutex); > > /* > * prototypes > @@ -497,6 +498,7 @@ snd_seq_oss_synth_sysex(struct seq_oss_devinfo *dp, > int dev, unsigned char *buf, > if (!info) > return -ENXIO; > > + guard(mutex)(&sysex_mutex); > sysex = info->sysex; > if (sysex == NULL) { > sysex = kzalloc(sizeof(*sysex), GFP_KERNEL); > > Hi, > > I did a lot of reproduction testing and it was very easy to reproduce before > the lock was added, after the lock was added the error was no longer > reproducible. Good to hear. Then I'm going to submit this as a band-aid fix; this is simple and easy to backport to older stable releases, too. Meanwhile, we may have a different fix for the long term. Essentially the sysex handling in OSS layer is unnecessarily complex, and we can send a packet immediately at each time instead of combining them. Could you try the patch below instead of the previous one? thanks, Takashi -- 8< -- diff --git a/sound/core/seq/oss/seq_oss_device.h b/sound/core/seq/oss/seq_oss_device.h index 98dd20b42976..c0b1cce127a3 100644 --- a/sound/core/seq/oss/seq_oss_device.h +++ b/sound/core/seq/oss/seq_oss_device.h @@ -55,7 +55,6 @@ struct seq_oss_chinfo { struct seq_oss_synthinfo { struct snd_seq_oss_arg arg; struct seq_oss_chinfo *ch; - struct seq_oss_synth_sysex *sysex; int nr_voices; int opened; int is_midi; diff --git a/sound/core/seq/oss/seq_oss_synth.c b/sound/core/seq/oss/seq_oss_synth.c index e3394919daa0..02a90c960992 100644 --- a/sound/core/seq/oss/seq_oss_synth.c +++ b/sound/core/seq/oss/seq_oss_synth.c @@ -26,13 +26,6 @@ * definition of synth info records */ -/* sysex buffer */ -struct seq_oss_synth_sysex { - int len; - int skip; - unsigned char buf[MAX_SYSEX_BUFLEN]; -}; - /* synth info */ struct seq_oss_synth { int seq_device; @@ -318,8 +311,6 @@ snd_seq_oss_synth_cleanup(struct seq_oss_devinfo *dp) } snd_use_lock_free(&rec->use_lock); } - kfree(info->sysex); - info->sysex = NULL; kfree(info->ch); info->ch = NULL; } @@ -395,8 +386,6 @@ snd_seq_oss_synth_reset(struct seq_oss_devinfo *dp, int dev) info = get_synthinfo_nospec(dp, dev); if (!info || !info->opened) return; - if (info->sysex) - info->sysex->len = 0; /* reset sysex */ reset_channels(info); if (info->is_midi) { if (midi_synth_dev.opened <= 0) @@ -408,8 +397,6 @@ snd_seq_oss_synth_reset(struct seq_oss_devinfo *dp, int dev) dp->file_mode) < 0) { midi_synth_dev.opened--; info->opened = 0; - kfree(info->sysex); - info->sysex = NULL; kfree(info->ch); info->ch = NULL; } @@ -482,63 +469,26 @@ snd_seq_oss_synth_info(struct seq_oss_devinfo *dp, int dev) /* * receive OSS 6 byte sysex packet: - * the full sysex message will be sent if it reaches to the end of data - * (0xff). + * the event is filled and prepared for sending immediately + * (i.e. sysex messages are fragmented) */ int snd_seq_oss_synth_sysex(struct seq_oss_devinfo *dp, int dev, unsigned char *buf, struct snd_seq_event *ev) { - int i, send; - unsigned char *dest; - struct seq_oss_synth_sysex *sysex; - struct seq_oss_synthinfo *info; + unsigned char *p; + int len = 6; - info = snd_seq_oss_synth_info(dp, dev); - if (!info) - return -ENXIO; + p = memchr(buf, 0xff, 6); + if (p) + len = p - buf + 1; - sysex = info->sysex; - if (sysex == NULL) { - sysex = kzalloc(sizeof(*sysex), GFP_KERNEL); - if (sysex == NULL) - return -ENOMEM; - info->sysex = sysex; - } - - send = 0; - dest = sysex->buf + sysex->len; - /* copy 6 byte packet to the buffer */ - for (i = 0; i < 6; i++) { - if (buf[i] == 0xff) { - send = 1; - break; - } - dest[i] = buf[i]; - sysex->len++; - if (sysex->len >= MAX_SYSEX_BUFLEN) { - sysex->len = 0; - sysex->skip = 1; - break; - } - } - - if (sysex->len && send) { - if (sysex->skip) { - sysex->skip = 0; - sysex->len = 0; - return -EINVAL; /* skip */ - } - /* copy the data to event record and send it */ - ev->flags = SNDRV_SEQ_EVENT_LENGTH_VARIABLE; - if (snd_seq_oss_synth_addr(dp, dev, ev)) - return -EINVAL; - ev->data.ext.len = sysex->len; - ev->data.ext.ptr = sysex->buf; - sysex->len = 0; - return 0; - } - - return -EINVAL; /* skip */ + /* copy the data to event record and send it */ + if (snd_seq_oss_synth_addr(dp, dev, ev)) + return -EINVAL; + ev->flags = SNDRV_SEQ_EVENT_LENGTH_VARIABLE; + ev->data.ext.len = len; + ev->data.ext.ptr = buf; + return 0; } /*